1. Field of the Invention
This invention relates to diaphragm devices for photographic cameras, video cameras, and the like.
2. Description of the Related Art
To begin, FIG. 10 to FIG. 12 show the conventional diaphragm device of a lens for a camera. A plurality of diaphragm blades 50 each have a pin 51 called the "fixed dowel" formed on one surface thereof, and another pin 52 called the "rotating dowel" formed on the other surface thereof. A diaphragm blade receptor 53 called the "beehive" (having a round opening 54 with its center at the optical axis) is provided with an equal number of holes 55 to the number of diaphragm blades 50 and accommodates the plurality of diaphragm blades 50 in such a way that the pins 51 are rotatably formed in the respective holes 55. A cam member 56 (having a round opening 57 with its center at the optical axis) also is accommodated in the interior of the diaphragm blade receptor 53. In the cam member 56 there are cut camming slots 58 for guiding the respective pins 52.
Therefore, when the diaphragm blade receptor 53 and the cam member 56 are rotated about the optical axis relative to each other, all the pins 52 move along the respective camming slots 58, while turning all the diaphragm blades 50 about the respective pins 51 in a space between the receptor 53 and the cam member 56. Depending on the overlapping amount of the turned diaphragm blades 50, the size of the opening of the aperture formed at the center by the inner edges of the diaphragm blades 50 is caused to vary. In such a manner, the amount of light passing through the aperture opening is adjusted.
Incidentally, in such a conventional diaphragm device, for the width W of the blade, determination of its value is made so that as the stopping down goes even to the minimum, light does not leak from any of the other edge portions than those defining the aperture opening. In other words, the blade in single form has to have both the function of determining the diameter of the aperture opening and the function of preventing light leakage at any point in the area other than the aperture opening. Because of this, the prior art could not reduce the width of the diaphragm blade to more than a certain extent.
For this reason, a much desired reduction of the size of the diaphragm blade receptor and the cam member, too, could not be done. This leads to the impossibility of reducing the outer diameter of the casing for the lens mounting having the diaphragm device incorporated therein any farther, thus giving one cause for inhibiting minimization of the size and weight of the lens barrel.